(Not Applicable)
(Not Applicable)
Electromagnetic radiation absorbent/shielding materials and structures are well-known. Such electromagnetic radiation absorbent/shielding materials and structures are commonly used in electromagnetic capability/electromagnetic interference (EMC/EMI) test cells to eliminate reflection and interference during testing. Electromagnetic radiation absorbent materials and structures are also utilized in electromagnetic anechoic chambers for testing high frequency radar, in antennas, and in Low Observable (LO) structures.
As those skilled in the art will appreciate, the construction of devices and structures utilizing such electromagnetic radiation absorbent/shielding materials may substantially reduce unwanted or stray electromagnetic radiation by absorbing/reflecting the electromagnetic radiation emitted by the device or incident upon the structure. In this respect, contemporary electromagnetic radiation absorbent/shielding materials function by absorbing/reflecting the electromagnetic radiation according to well-known principles.
Although various materials have been found to be suitable for use in such electromagnetic absorbent/shielding structures, a problem that frequently arises concerns the treatment of gaps that are frequently formed by intermediate adjacent structural members, such as structural panels or coverings. In this regard, it is recognized that such gaps may contribute substantially to the undesirable reflection of electromagnetic radiation.
Thus, in order to reduce the reflected by a gap, it is necessary to fill the gap with an electromagnetic radiation reflective material. To that end, namely, to mitigate electromagnetic radiation reflection from such gaps between adjacent electromagnetic radiation panels and the like, conventional methodology dictates the use of a conductive filler, which is typically known to comprise nickel-coated inclusions designed to produce a material with maximum DC conductivity.
While such contemporary conductive gap fillers have proven generally suitable for their intended use, the same nonetheless possess inherent deficiencies which tend to detract from their overall desirability. Such inherent deficiencies particularly detract from the usefulness of such gap fillers in the repair and maintenance of LO aircraft. Specifically, replacement of gap treatments for frequently removed/opened access doors and panels takes too long, dependent on cure time of caulks and tapes. Lack of performance in four areas also occurs, namely: (1) some caulks are not conductive enough, due either to less conductive fillers, or less volume % loading; (2) extension and elasticity at xe2x88x9267xc2x0 F. are too low; (3) resistance of gap fillers to aircraft fluids has been less than desired, often when using xe2x80x9cacceleratedxe2x80x9d cures which are incomplete and thus susceptible to solvent-induced swell; and (4) adhesion and crack resistance are often low.
In this regard, it is recognized that most prior art conductive fillers fail to attain both properties of effective electric permittivity, on one hand, and resilient mechanical/material properties, on the other. The latter property is especially important when such gap fillers are utilized in LO aircraft maintenance due to the harsh environment to which such fillers will be subjected, which necessarily requires that such filler possess sufficient material durability and reliability.
Accordingly, there is a substantial need in the art for a highly conductive gap filler that possesses sufficient durability and reliability such that the same may be utilized in repair and maintenance of LO aircraft in the field. There is a further need in the art for such gap fillers that, in addition to possessing both effective electric permittivity and mechanical properties, can be readily formulated and utilized using conventional, commercially available materials.
The present invention specifically addresses and alleviates the above-identified deficiencies in the art. In this regard, the present invention is directed to a highly conductive thermoplastic elastomer (TPE) that is particularly useful, among other things, for use in the repair and maintenance of LO aircraft in the field. According to a preferred embodiment, the gap filler comprises graphite fiber coated with a nickel-copper-nickel coating suspended within a suitable elastomer, such as polyvinylchloride (PVC). Preferably, the graphite fiber has a diameter ranging from 4 to 10 microns with 7 being preferred, and a length ranging from 0.032 to 0.060 inches. The nickel-copper-nickel coated graphite fiber is added to the elastomer such that the fiber comprises approximately 11.1% or less by weight of the resultant elastomer or, alternatively, approximately 5.39% or less by volume of the elastomer. Preferably, the resultant elastomer has a density of approximately 1.37 g/cm3. The gap filler may optionally include carbon black filler, which may be corded along with the graphite fiber, and may be present in amounts up to 14.00% by weight or 12.00% by volume of such gap filler. The resultant elastomer can advantageously attain any level of desirable EMI shielding, while at the same time possessing sufficient flexibility at reduced temperatures and withstand aircraft fluids and the like and, as such, possesses desirable durability necessary for use in LO aircraft repair and maintenance applications.